This invention relates to multi-speed transmissions and more particularly to a family of transmissions employing three planetary gear sets and five torque transmitting mechanisms to provide at least six forward speed ratios and a reverse ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978, U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000, U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992, and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three and four speed automatic transmissions and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and another reverse ratio. The Lepelletier employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining two planetary gear sets.
It is an object of the present invention to provide an improved family of multi-speed transmission having three planetary gear sets and five torque transmitting mechanisms.
In one aspect of the present invention, the three planetary gear sets each have three members that are a sun gear member, a ring gear member and a planet carrier assembly member. In another aspect of the present invention, an input shaft is continuously connected with one member of one of the planetary gear sets. In yet another aspect of the present invention, the planetary gear set to which the input shaft is continuously connected may be of either the simple or compound type. In still another aspect of the present invention, a first member of each of a first and second of the planetary gear sets are continuously interconnected, a second member of the planetary gear sets are also continuously interconnected, and a first member of the third planetary gear set is continuously connected with a stationary portion of the transmission.
In yet still another aspect of the present invention, an output shaft is continuously connected with a member of one of the planetary gear sets. In a further aspect of the present invention, the five torque transmitting mechanisms are either five selectively engageable rotating torque transmitting mechanisms (clutches) or four rotating torque transmitting mechanisms and one selectively engageable stationary torque transmitting mechanism (brake). In a yet further aspect of the present invention, a first and second of the rotating torque transmitting mechanisms selectively connect the second member of the third planetary gear set with members of the first or second planetary gear sets, a third of the rotating torque transmitting mechanisms selectively connects the third member of the third planetary gear set with members of the first or second planetary gear sets, and a fourth of rotating torque transmitting mechanisms selectively connects the first or third member of the third planetary gear set with a member of the first or second planetary gear sets. In a still further aspect of the present invention, the fifth torque transmitting mechanism selectively connects a member of the first or second planetary gear set with either a member of the third planetary gear set or with a stationary portion of the transmission.
The present invention presents a family of multi-speed transmissions having three planetary gear sets and five selectively engageable torque transmitting mechanisms comprised of either five clutches or four clutches and one brake. Each of the planetary gear sets has first, second, and third members including a sun gear member, a ring gear member, and a planet carrier assembly member. The planet carrier assembly member can be of the single pinion (simple) type or the double pinion (compound) type.
A first and second members of the first planetary gear set are continuously interconnected with respective first and second members of the second planetary gear set. A first member of the third planetary gear set is continuously connected to ground (transmission case). The input and output shafts are continuously connected with the continuously interconnected members or with other members of the planetary gear sets.
A first and second of the torque transmitting mechanisms selectively interconnect the second member of the third planetary gear set with members of the first or second planetary gear set. A third of the torque transmitting mechanisms selectively interconnects the third member of the third planetary gear set with members of the first or second planetary gear set. A fourth of the torque transmitting mechanisms selectively interconnects the first or third member of the third planetary gear set with a member of the first or second planetary gear set. A fifth of the torque transmitting mechanisms either selectively interconnects a member of the first or second planetary gear set with a member of the third planetary gear set, or selectively connects a member of the first or second planetary gear set to the transmission case. The five torque transmitting mechanisms are selectively engaged in combinations of two to establish six forward speed ratios and one reverse speed ratio between the input and output shafts of the transmissions.